The invention disclosed and claimed herein pertains to the field of digital electronics systems. More particularly, the invention pertains to digital systems within which information is transferred in a time-division multiplexed format. More particularly still, the invention pertains to such systems within which time domain multiplexed information is transferred between equipments upon a common conduction path, commonly called a data bus.
A useful technique of transmitting digital information between the units of a digital electronic system involves the use of a single, common transmission line called a data bus. Access to the bus for purposes of transmission is a feature of the system control mechanism which governs use of the bus. Many system control mechanism utilize time-domain multiplexing to allocate transmission access time.
Time-domain multiplexing refers to the designation of discrete, coherent time slots for use as communication channels. This technique is applied to data bus transmission by allowing a respective system unit access to the bus during an allocated time slot.
Demultiplexing of information which is transmitted on the bus is accomplished by observing the transmission on the bus during the time slot of interest.
Such data bus multiplexing techniques assign time slots on a complete word or message basis. Control over assignment of and access to the time slots requires a sophisticated level of system control. Control may be lodged in a centralized system controller, or shared between a less sophisticated controller and data bus users.
The sophisticated data bus control techniques of the prior art require additional system hardware and software to process the control information. Bus data transmission efficiency, the portion of transmission time devoted to movement of data, is reduced by the dedication of separate transmission time slots for control information traffic alone. On a system basis, cost per data unit transmitted is directly related to dedicated elements and to bus transmission efficiency. Hence, minimization of control equipment and maximization of efficiency are mandatory for low cost data transfer.